1. Field of the Invention
The present invention relates to a piezoelectric ceramic composition, and more particularly to a piezoelectric ceramic composition useful as a material for producing piezoelectric ceramic elements such as piezoelectric ceramic filters and piezoelectric ceramic oscillators.
2. Background Art
Piezoelectric ceramic compositions predominantly comprising lead titanate zirconate (Pb(Ti.sub.x Zr.sub.1-x, O.sub.3) or lead titanate (PbTiO.sub.3) have been widely used for the production of piezoelectric ceramic elements such as piezoelectric ceramic filters and piezoelectric ceramic oscillators. Piezoelectric ceramic compositions predominantly comprising lead titanate zirconate or lead titanate are generally produced by use of lead oxides, which cause a reduction in homogeneity of products due to evaporation of lead oxides. In contrast, piezoelectric ceramic compositions predominantly comprising a layered bismuth compound represented by (Sr.sub.1-x M.sub.x)Bi.sub.2 Nb.sub.2 O.sub.9 contain no lead oxide and therefore do not introduce this type of problem.
However, piezoelectric ceramic compositions predominantly comprising a layered bismuth compound have a small electromechanical coupling coefficient kt and therefore have not yet been widely used in practice.